1. Field of the Invention
The present invention relates to a method of removing a photo-resist layer on a semiconductor wafer, and more particularly, to a method of removing a photo-resist layer in an environment without oxygen.
2. Description of the Prior Art
In the dual-damascene process of semiconductor, the metallic wire is formed within the inter-metal dielectrics (IMD) to connect the transistor and other devices on the semiconductor wafer. The formation of the metallic wire comprises forming a photo-resist layer on the IMD of the semiconductor wafer by using the photolithography process to define a recess or a contact hole. Then, the photo-resist layer is removed, and a metallic layer is formed in the recess or the contact hole to function as a metallic wire. The prior art method of removing the photo-resist layer destroys the profile of the recess or the contact hole and affects the subsequent process. Therefor, the method of removing the photo-resist layer must be improved in order to keep the quality of the dual-damascene process.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior art method of forming a contact hole 22 on a semiconductor wafer 10. A prior art contact hole 22 is formed on an IMD 18 of a semiconductor wafer 10. The IMD 18 comprises a barrier layer 12, a dielectric layer with a low k (dielectric constant) 14, and a cap layer 16. The barrier layer 12 is made of SiN, SiON, or SiC, the dielectric layer with a low k 14 is made of fluorine-rich silicate glass, and the cap layer 16 is made of SiO, SiN, SiON or SiC. The dielectric constant (k) of the dielectric layer with a low k 14 is less than the dielectric constant of the barrier layer 12 and the cap layer 16.
The prior art method of forming the contact hole 22 in the IMD 18 comprises coating a photo-resist layer on the IMD 18, and performing a lithography and an etching processes to remove the IMD 18 whetein the IMD 18 not covered by the photo-resist layer is removed to a predetermined thickness. That means to remove the cap layer 16, the dielectric layer with a low k 14 and the barrier layer 12 to form the contact hole 22. Then, a cleaning process is performed to completely remove the photo-resist layer. The formation of the metallic wire by filling the contact hole 22 with metallic materials is then followed.
In the cleaning process according to the prior art, first a dry ashing process is performed by injecting oxygen as reactive gases of the plasma chemical reaction to remove most of the photo-resist layer. Next, organic or inorganic solution is utilized for damaging the structure of the photo-resist layer to completely remove the remaining photo-resist layer. During the dry ashing process, oxygen plasma reacts with the dielectric layer with a low k 14 to form a bowl-shape contact hole 22, as shown in FIG. 1. The metallic materials can not completely fill the bowl-shape contact hole 22. Consequently, the metallic wire with voids insides is formed, which affect the electric performance of the semiconductor wafer 10. Besides, the dielectric constant of the dielectric layer with a low k 14 will be changed by oxygen plasma, so that the insulation of electric signal of the IMD 18 will be reduced.
It is therefore a primary objective of the present invention to provide a method of removing a photoresist layer from a semiconductor wafer to solve the above mentioned problems.
In a preferred embodiment, the present invention relates to a method of removing a photo-resist layer from a semiconductor wafer, the semiconductor wafer comprising an inter-metal dielectric layer, and a photo-resist layer positioned on the inter-metal dielectric layer, the method comprising:
performing a dry cleaning process by injecting a nitrogen-containing gas into an oxygen-free environment and utilizing a plasma reaction to remove most of the photo-resist layer; and
performing a wet cleaning process to completely remove the photo-resist layer.
It is an advantage of the present invention that the cleaning process can avoid the contact hole being etched to form a blow-shape hole and the dielectric constant of the dielectric layer with a low k being changed.
These and other objective of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.